AD 99-04-01

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that requires repetitive inspections of the outboard nacelle struts to detect fatigue cracking of the strut skin and spring beam support fittings, and to detect cracked or loose fasteners of the support fittings; and corrective actions, if necessary. This amendment also provides for optional terminating action for the repetitive inspection requirements. This amendment is prompted by reports indicating that several cracked or broken spring beam support fittings were found on the outboard nacelle struts. The actions specified by this AD are intended to detect and correct such fatigue cracking and loose fasteners, which could result in failure of the outboard nacelle struts and consequent separation of the engine.

Final rule.

99-04-01 BOEING: Amendment 39-11025. Docket 98-NM-144-AD. \n\n\tApplicability: Model 747 series airplanes, line numbers 202 through 886 inclusive, equipped with General Electric Model CF6-45/50 and Pratt & Whitney Model JT9D-70 series engines; on which the strut/wing modification has not been accomplished in accordance with AD 95-13-07, amendment 39-9287; certificated in any category. \n\n\tNOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been otherwise modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (h) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo detect and correct fatigue cracking of the strut skin and spring beam support fittings on the outboard nacelle struts, and cracked or loose fasteners of the support fittings, which could result in failure of the outboard nacelle struts and consequent separation of the engine, accomplish the following: \n\n\t(a)\tPrior to the accumulation of 13,000 total flight cycles, or within 6 months after the effective date of this AD, whichever occurs later, perform a detailed visual inspection of the outboard nacelle struts, as specified by paragraphs (a)(1), (a)(2), (a)(3), and (a)(4) of this AD, in accordance with Boeing Alert Service Bulletin 747-54A2172, dated February 23, 1995, or Boeing Service Bulletin 747-54A2172, Revision 1, dated January 4, 1996. \n\n\t\t(1)\tInspect the spring beam support fittings to detect cracks of the support fittings.\n \n\t\t(2)\tInspect the spring beam support fittings at the fasteners, using a borescope to detect cracks of the support fittings. \n\n\t\t(3)\tInspect the fasteners of the outer spring beam support fittings to detect cracked or loose fasteners. \n\n\t\t(4)\tInspect the strut skin to detect cracks. \n\n\t(b)\tIf no discrepancy is found during any inspection required by paragraph (a) of this AD, perform detailed visual inspections of the outboard nacelle struts to detect any discrepancies specified in paragraphs (b)(1), (b)(2), (b)(3), and (b)(4) of this AD, in accordance with Boeing Alert Service Bulletin 747-54A2172, dated February 23, 1995; or Boeing Service Bulletin 747-54A2172, Revision 1, dated January 4, 1996. Perform the inspection at the times specified in paragraph (c) or (d) of this AD, as applicable. \n\n\t\t(1)\tPerform a detailed visual inspection, using a borescope, of only the outer spring beam support fittings atthe fasteners through the horizontal flange to detect cracks of the support fittings. \n\n\t\t(2)\tPerform a detailed visual inspection, using a borescope, of the fasteners through the vertical flange of only the outer spring beam support fittings to detect loose collars. \n\n\t\t(3)\tPerform an external detailed visual inspection of only the outer spring beam support fittings to detect cracked or loose fastener heads. \n\n\t\t(4)\tPerform a detailed visual inspection of the strut skin to detect cracks. \n\n\t(c)\tFor Model 747-SR series airplanes equipped with General Electric Model CF6-45 series engines, on which no discrepancy is found during any inspection required by paragraph (a) of this AD: Perform the inspection required by paragraph (b) of this AD within 1,600 flight cycles following the accomplishment of the inspection required by paragraph (a) of this AD; and thereafter at intervals not to exceed 1,600 flight cycles until accomplishment of the optional terminating action specified inparagraph (g) of this AD. \n\n\t(d)\tFor Model 747 series airplanes other than those identified in paragraph (c) of this AD, on which no discrepancy is found during any inspection required by paragraph (a) of this AD: Perform the inspection required by paragraph (b) of this AD within 1,000 flight cycles following the accomplishment of the inspection required by paragraph (a) of this AD; and thereafter at intervals not to exceed 1,000 flight cycles until accomplishment of the optional terminating action specified in paragraph (g) of this AD. \n\n\t(e)\tIf any cracking is found in the spring beam support fittings during any inspection required by this AD, prior to further flight, replace the support fitting with a new support fitting, in accordance with the Accomplishment Instructions in Part IV. of Boeing Service Bulletin 747-54A2172, Revision 1, dated January 4, 1996. Accomplishment of this replacement constitutes terminating action for the repetitive inspection requirements of this ADfor only the new support fitting. Continue the repetitive inspections required by paragraph (b) of this AD for the other support fitting locations until accomplishment of the terminating action specified by paragraph (g)(1) or (g)(2) of this AD, as applicable. \n\n\t(f)\tIf any crack is found on the strut skin, or if any cracked or loose fastener or collar is found during any inspection required by this AD, prior to further flight, repair in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate; or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative who has been authorized by the Manager, Seattle ACO, to make such findings. \n\n\t(g)\tAccomplishment of an open-hole high frequency eddy current (HFEC) inspection, in accordance with Boeing Alert Service Bulletin 747-54A2172, dated February 23, 1995, or Boeing Service Bulletin747-54A2172, Revision 1, dated January 4, 1996; and either paragraph (g)(1) or (g)(2) of this AD, as applicable; constitutes terminating action for the requirements of this AD. \n\n\t\t(1)\tIf no discrepancy is found during the HFEC inspection, prior to further flight, rework the fastener holes and install new fasteners, in accordance with Figures 6 and 7 of Boeing Alert Service Bulletin 747-54A2172, dated February 23, 1995, or Boeing Service Bulletin 747-54A2172, Revision 1, dated January 4, 1996. \n\n\t\t(2)\tIf any cracking is found during the HFEC inspection, prior to further flight, replace any cracked spring beam support fitting with a new support fitting, in accordance with Part IV. of the Accomplishment Instructions specified by Boeing Service Bulletin 747-54A2172, Revision 1, dated January 4, 1996.\n\n\t(h)\tAn alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO. \n \n\tNOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO. \n\n\t(i)\tSpecial flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished. \n\n\t(j)\tExcept as provided by paragraph (f), (g), (g)(1), and (g)(2) of this AD, the actions shall be done in accordance with Boeing Alert Service Bulletin 747-54A2172, dated February 23, 1995, and Boeing Service Bulletin 747-54A2172, Revision 1, dated January 4, 1996, as applicable. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC. \n\n\t(k)\tThis amendment becomes effective on March 16, 1999.

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to certain Boeing Model 747 series airplanes was published in the Federal Register on November 24, 1998 (63 FR 64913). That action proposed to require repetitive inspections of the outboard nacelle struts to detect fatigue cracking of the strut skin and spring beam support fittings, and to detect cracked or loose fasteners of the support fittings; and corrective actions, if necessary. That action also proposed to provide for optional terminating action for the repetitive inspection requirements. \n\n\tInterested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the single comment received. \n\n\tThe commenter supports the proposed AD. \n\nConclusion \n\n\tAfter careful review of the available data, including the comment noted above, the FAAhas determined that air safety and the public interest require the adoption of the rule as proposed.\n\n Cost Impact \n\n\tThere are approximately 145 Model 747 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 9 airplanes of U.S. registry will be affected by this AD, that it will take approximately 16 work hours per airplane to accomplish the required inspection, and that the average labor rate is $60 per work hour. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $8,640, or $960 per airplane, per inspection cycle. \n\n\tThe cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. \n\n\tShould an operator elect to accomplish the fastener hole inspection and modification, it would take approximately 20 work hours (excluding removal of thestrut and spring beam) to accomplish it, at an average labor rate of $60 per hour. Based on these figures, the cost impact of this optional terminating action is estimated to be $1,200 per strut. \n\n\tShould an operator elect to accomplish the replacement of the spring beam support fittings with new support fittings, it would take approximately 108 work hours (excluding removal of the strut and spring beam) to accomplish it, at an average labor rate of $60 per hour. Based on these figures, the cost impact of this optional terminating action is estimated to be $6,480 per support fitting. \n\nRegulatory Impact \n\n\tThe regulations adopted herein will not have substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalismimplications to warrant the preparation of a Federalism Assessment. \n\n\tFor the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES." \n\nList of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \nAdoption of the Amendment \n\n\tAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:\n\n PART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701. § 39.13 (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: